[Django]-Django Admin nested inline

There has been some movement in https://code.djangoproject.com/ticket/9025 recently, but I wouldn’t hold my breath.

One common way around this is to link to an admin between first and second (or second and third) level by having both a ModelAdmin and an Inline for the same model:

Give Certificate a ModelAdmin with TrainingDate as an inline. Set show_change_link = True for CertificateInline so you can click on an inline to go to its ModelAdmin change form.

admin.py:

# Certificate change form has training dates as inline

class TrainingDateInline(admin.StackedInline):
    model = TrainingDate

class CertificateAdmin(admin.ModelAdmin):
    inlines = [TrainingDateInline,]
admin.site.register(Certificate ,CertificateAdmin)

# Person has Certificates inline but rather
# than nesting inlines (not possible), shows a link to
# its own ModelAdmin's change form, for accessing TrainingDates:

class CertificateLinkInline(admin.TabularInline):
    model = Certificate
    # Whichever fields you want: (I usually use only a couple
    # needed to identify the entry)
    fields = ('cerfificate_no', 'certificate_date')
    # Django 1.8 introduced this, no need to make your own link
    show_change_link = True

class PersonAdmin(admin.ModelAdmin):
    inlines = [CertificateLinkInline,]
admin.site.register(Person, PersonAdmin)

More universal solution

from django.utils.safestring import mark_safe
from django.urls import reverse

class EditLinkToInlineObject(object):
    def edit_link(self, instance):
        url = reverse('admin:%s_%s_change' % (
            instance._meta.app_label,  instance._meta.model_name),  args=[instance.pk] )
        if instance.pk:
            return mark_safe(u'<a href="{u}">edit</a>'.format(u=url))
        else:
            return ''

class MyModelInline(EditLinkToInlineObject, admin.TabularInline):
    model = MyModel
    readonly_fields = ('edit_link', )

class MySecondModelAdmin(admin.ModelAdmin):
    inlines = (MyModelInline, )

admin.site.register(MyModel)
admin.site.register(MySecondModel, MySecondModelAdmin)

pip install django-nested-inline

This package should do what you need.

A more up-to-date solution (february 2021) is to use the show_change_link config variable: https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.InlineModelAdmin.show_change_link

This does exactly the same as the EditLinkToInlineObject proposed in solutions above, but is less code and is probably well tested by Django Developers

You would just have to define show_change_link=True in each one of your inlines

Nested inlines are provided at:
https://github.com/BertrandBordage/django-super-inlines/

pip install django-super-inlines

Use django-nested-admin which is the best package to do nested inlines.

First, install "django-nested-admin":

pip install django-nested-admin

Then, add "nested_admin" to "INSTALLED_APPS" in "settings.py":

# "settings.py"

INSTALLED_APPS = (
    # ...
    "nested_admin", # Here
)

Then, add "path(‘_nested_ad…" to "urlpatterns" in "urls.py":

# "urls.py"

from django.urls import include, path

urlpatterns = [
    # ...
    path('_nested_admin/', include('nested_admin.urls')), # Here
]

Finally, extend "NestedTabularInline" with "Training_DateInline()" and "CertificateInline()" classes and extend "NestedModelAdmin" with "PersonAdmin()" class in "admin.py" as shown below:

# "admin.py"

from .models import Training_Date, Certificate, Person
from nested_admin import NestedTabularInline, NestedModelAdmin

class Training_DateInline(NestedTabularInline):
    model = Training_Date

class CertificateInline(NestedTabularInline):
    model = Certificate
    inlines = [Training_DateInline]

@admin.register(Person)
class PersonAdmin(NestedModelAdmin):
    inlines = [CertificateInline]

I used the solution provided by @bigzbig (thank you).

I also wanted to go back to the first list page once changes had been saved so added:

class MyModelInline(EditLinkToInlineObject, admin.TabularInline):
    model = MyModel
    readonly_fields = ('edit_link', )

    def response_post_save_change(self, request, obj):
        my_second_model_id = MyModel.objects.get(pk=obj.pk).my_second_model_id
        return redirect("/admin/mysite/mysecondmodel/%s/change/" % (my_second_model_id))